The invention relates to a semiconductor device provided with a number of programmable elements which each comprise a conductor region and a doped semiconductor region separated from one another by an insulating layer, while the conductor region comprises a material which is suitable for forming a rectifying junction with the material of the semiconductor region, the said elements being arranged in a matrix of rows and columns in which within one row the conductor regions of the programmable elements are coupled to a common row conductor and within one column the semiconductor regions of the programmable elements are coupled to a common column conductor, which device is provided with programming means for applying a programming voltage for programming of an element between the column conductor and row conductor associated with this element, which voltage is greater than the breakdown voltage of at least a portion of the insulating layer situated between the conductor region and the semiconductor region of the element.
Such a device is known from U.S. Pat. No. 4,881,114. In the known device, the programmable elements form part of a memory matrix comprising a number of rows and columns of programmable memory elements. The columns of the matrix are provided with column conductors by which the semiconductor regions of the elements situated therein are coupled to one another. The column conductors are formed by elongate surface zones which were provided in a semiconductor substrate through diffusion. Similarly, the rows of the matrix are provided with row conductors by which the conductor regions of the programmable elements in one row are connected to one another. The row conductors in the known device comprise conductor tracks of polycrystalline silicon and extend in a direction transverse to the surface zones. The conductor tracks and surface zones are doped so as to have mutually opposing conductivity types and are separated from one another by a comparatively thin insulating silicon oxide layer. In this way, at each intersection of a row conductor with a column conductor a programmable element is located the conductor region of which element forms part of a conductor track and the semiconductor region of which element forms part of a surface zone.
For programming such an element, the known device is provided with programming means with which a programming voltage of the order of 30 V is applied between the column conductor and row conductor associated with the element to be programmed during a comparatively short pulse of less than 100 ms. The insulating silicon oxide layer is punctured locally by such a voltage, so that the semiconductor region and the conductor region of the element come into mutual contact and a rectifying junction is formed between them. The result is that the series resistance of the element at least in the forward direction of the formed junction changes permanently from a comparatively high value to a comparatively low value, which represents the memory contents of the element.
When an element is programmed in this way, it should be ensured that other, non-addressed elements of the matrix do not also get programmed. This latter effect can be counteracted in that a voltage difference different from the programming voltage is applied between the column and row conductors associated with the other elements. A disadvantage of this is, however, that additional measures are to be taken for generating such a different voltage level, especially where the programming means are concerned.
Furthermore, it is important for a satisfactory operation of the device that the rectifying junction formed after programming should have a comparatively good and reproducible diode characteristic.